The acute and chronic toxicity of malonaldehyde (MA), a reportedly carcinogenic product of lipid peroxidation in foods and in vivo, will be evaluated in animals and in cell cultures. MA will be administered to Swiss female mice at levels of 0.1, 1.0 and 10.0 microgram/g body weight/day for one year. Complete hematology and histopathology will be performed, with emphasis on liver, pancreas and bladder, in which nuclear changes were seen previously in mice given larger doses of MA for 92 days. All tissues will be examined for evidence of tumors and selected organs will be analyzed for lipofuscin pigments. The acute oral LD50 and NED50 of MA will be determined in mice and rats. Rat skin fibroblasts, rat hepatocytes and human lymphocytes will be used to determine the effect of MA on cell and nuclear morphology, chromosome structure, nucleic acid metabolism and protein synthesis. The binding of 14C-MA by DNA, RNA and protein will be investigated using pure compounds and cell cultures in an effort to determine the nature of the bonds formed with MA by these substances in vivo. Previous studies on the metabolism of 14C-MA by rat liver mitochondria will be extended to elucidate more clearly the pathway of metabolism of this compound and to identify the intermediary products.